1. Technical Field
The invention relates to an apparatus and method for simultaneously determining the viscosity and density of a fluid.
2. Description of Related Art
A number of apparatus and methods exist for measuring the density or viscosity of a fluid. U.S. Pat. Nos. 2,348,732 and 2,348,733 to Fischer and 2,800,019 to Rumble and British Pat. No. 780,932 to Vereinigte Glanzstoff-Fabriken A. G. employ a float within a vertically tapered tube to determine the viscosity or density of a flowing fluid. U.S. Pat. No. 2,426,393 to Fischer discloses an apparatus for measuring the viscosity of a fluid by comparing the relative position of two floats in a tube.
Other common apparatus for determining the viscosity of a fluid include falling ball, rolling ball and capillary tube viscometers. Falling and rolling ball viscometers do not determine absolute viscosity, but kinematic viscosity which is the ratio of the absolute viscosity to the density of the fluid. The apparatus have limited accuracy and range. They are subject to fouling, especially when used with crude oils that precipitate paraffinic or asphaltic materials.
Capillary tube viscometers are difficult to use with different fluids because of problems with cleaning and the long times required to reach equilibrium when changing fluids. The apparatus are extremely sensitive, especially at high line pressures, and require precise calibration of the differential pressure transducer which is often a source of error.
An alternative apparatus and method from those described above are needed for determining the viscosity and density of a fluid. An apparatus and method are needed which are accurate and easy to use, especially at high pressure and temperature.